A lens is a transparent piece of material that focuses or scatters light rays to create or alter images. A lens can be thought of as a curved disc: depending on whether it is curved outward or inward, it can collect light (convex) or scatter it (concave).
Lenses are used in many everyday devices: in glasses, microscopes, cameras, binoculars, and projectors to make images sharp or magnify them. With the right shape of lens, light rays can be directed so that we can see clear, magnified, or reduced images.